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When does ASME apply?

Rocky_3 Member Posts: 231
Greetings, Wet-Heads.
Seeing as I am a boiler guy, and not a plumber-guy, I have a question that I have never been able to get a satisfactory answer for and thought I would try this fine resource. When does a domestic hot water system require an ASME rated thermal expansion tank versus a non-ASME tank? Scenario I am looking at is an oil-fired Bock 190-E (113 gallons storage, 190,000 BTU input) makes the hot water and a separate 120 gallon ASME rated storage tank stores it at 120 degrees. This gives a total of 230 gallons storage, but only 190K input. Condo Association is the type of building (boiler/hot water systems in a detached mechanical building). Obviously the owner wants to know if he needs an ASME rated tank or not as there is literally 17 times the price difference between an ST-12, and an ST-12C ASME. I have yet to find any definitive literature or answer as to what determines whether a thermal expansion tank needs to be ASME rated or not. Any help for my own edification would be greatly appreciated.
Warm regards from chilly Fairbanks (yes, its snowing today),


  • rick in Alaska
    rick in Alaska Member Posts: 1,362
    I can't remember on the storage issue, or if it even applies when it is not all in one tank, but as far as the heating system, I am pretty sure it is anything over 199,000 btu. I stay away from commercial, so not quite sure of this.
    Warm regards from sunny Homer ( 32 and nice). B)
  • delta T
    delta T Member Posts: 870
    My experience with our state boiler inspector was that, at least on the boiler side, if the relief valve was more than 30 psi for the boiler, the expansion tank had to be asme, but 30 or less it did not. He didn't seem to care about the btu input as some of these boilers were over 1,000,000 input. As far as the DHW side of things goes, I don't have an answer for you. I would try calling your local AHJ and see what they want.
  • bob_46
    bob_46 Member Posts: 813
    Always, Sometime, Maybe, Except.
  • jumper
    jumper Member Posts: 1,833
    ASME stamps are to be avoided when allowed. Otherwise B & M insurance inspector may ask you to test device someday.
    EBEBRATT-Ed Member Posts: 11,992
    @delta T is correct. Under 30psi non asme over 30 asme for a heating system expansion tank.

    DHW, not sure.
  • hot_rod
    hot_rod Member Posts: 16,289
    A good question for your Amtrol rep

    Inspectors interpretation are usually the biggest unknown

    Stay warm, spring will arrive
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EBEBRATT-Ed Member Posts: 11,992
    @hot rod agree about the inspectors, as far as spring being here soon.........not so much!! LOL
  • Henry
    Henry Member Posts: 995
    Storing hot water at 120F is a no-no. You risk bacteria etc. Legionnaire survives up to 139F.
  • bob eck
    bob eck Member Posts: 929
    I was told if water heater is under 199,000 BTU input and storage tank is under 120 gallons it is non ASME.
    That is why they make a 199,000 BTU input water heater that has 119 gallon storage.
    But you still need to check with the local inspector that can over rule everything and it could come down to that inspector.
    If you have more than one water heater and more than one storage tank that could be different.
    Check with local code.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    3 factors dictate ASME for DHW heating. If the appliance has an input greater than 199K, has a volume greater than 120 gallons, or holds water temperatures greater than 180 degrees F. If any ONE of these parameters is exceeded, the vessel has to be ASME rated.

    In response to Bob's Always, Sometimes, Maybe, Except interpretation, I submit A Substantial Monetary Exchange :smile:

    As it pertains to placement, I've always assumed that if it is a commercial/public application, including apartment complexes, restaurants etc, that ASME applies, but that is my personal take, and not something I know for a fact. That's just the only time I've been called on it by the AHJ. That and if you have to install an ASME rated water heater, than it makes sense to require an ASME expansion tank.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Rocky_3
    Rocky_3 Member Posts: 231
    Thanks, Mark. Clearest explanation I've heard of yet. Appreciate your time.
  • jumper
    jumper Member Posts: 1,833
    So if you have the room does it make sense to use multiple domestic instead of commercial?
  • Rocky_3
    Rocky_3 Member Posts: 231
    Condo Association already bought the 120 gallon ASME rated storage tanks. We are just quoting to install them (replacing existing tanks that have/are failing).
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    jumper said:

    So if you have the room does it make sense to use multiple domestic instead of commercial?

    If any one of the three parameters are exceed, then all vessels must be ASME. So if you have two 80 gallon tanks in parallel, and only 190K btuH output, and operate at 140 degrees, the tanks have to be ASME because the aggregate volume exceeds 119 gallons. Or at least that's what the Colorado boiler inspector made me do in order to comply...

    And you're welcome Rocky. Glad I could help.


    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • dopey27177
    dopey27177 Member Posts: 873
    As an contractor of record in all commercial, industrial and apartment house installations for your own safety install the ASME rated tank.

    God forbid something goes awry the lawyers use a shot gun approach to find some one liable.

    A shot gun approach is all the contractors that work in the building get put up on a wall, the lawyer takes his shot gun loaded with bird shot and fires. Wherever a pellet hits that is the guys that get sued.

    One thing you need to know many local agencies have some jurisdiction in a building. Each one has there own mechanical requirements. One agency may have an obscure out of date rule that a lawyer can attach to you. Then tag you are it.

    When you take the higher spec you will always be safe from having the finger on you.

    I was a consultant for 10 years and had that experience. All my work had made notice to the customer where problems in their plant existed in the locations I worked in and a disclaimer in my reports worked well for me.

    My liability insurer loved me because I was covered as a consultant by making note of problems I saw. Additionally I had an error of omission and commission clause in my contract with the customer. Thereby being held harmless in any law suit.

    My insurers lawyers stopped any possible lawsuit that could be made.

    The best thing about that my insurance costs were lowered.

    Jacob Myron
  • Mike_Sheppard
    Mike_Sheppard Member Posts: 682
    @dopey27177 that is some great information. I am working towards my own company and I love getting some solid advice like that.

    Also, love your book! Has been helping me for years.
    Never stop learning.